Rotor blade damper



Nov. 4, 1952 Filed Nov. 7, 1947 F'IG. I

J. RZECZYCKI ROTOR BLADE DAMPER 3 Sheets-Sheet l y INVENTOR.

Nov. 4, 1952 J. RzEczYcKl 2,616510 Ro'roR BLADE DAMPER Filed Nov. 7, 1947 a snees-snee'z 2' l |I I' l l l l 1 ||1|| JN VEN TOR.

3 Sheets-Sheet S J. RzEczYcKl Ro'roR BLADE DAMPER Nov. 4, 1952 FnedvNov. 7, 1947 Patented Nov. 4, 12952 ROTOR BLADE DAMPER JosephlRzeczycki, Philadelphia, Pa., assignor, by

mesne assignments, to Piasecki Helicopter Corporation, Morton, Pa., a corporation of Pennsylvania Application November 7, 1947, Serial No. 784,614

Claims. (Cl. 170- 160.55)

This invention relates to rotary wing aircraft and more specifically to devicesv used to dampen oscillations of rotor blades about their Vertical pivots.

In the operation of rotary Wing aircraft employing articulated rotors it is common practice to use hydraulic dampers to prevent violent oscillation of the rotor blades in their plane of rotation. This violent oscillation usually occurs when the rotors are being stopped or started and the rotor speed is Somewhere over one third of the normal rpm of the rotor.

I have found that during the period of time after theA rotor is first started and until it reaches approximately vone third of its normal speed, that the type of damper now employed will allow the blades to lag back about the Vertical hinge, placing high loads on the control system, as the centrifugal force generated at these W speeds is not great enough to maintain the blades in their normal radial position. This condition also presents itself again when the rotor is being stopped, except in the latter condition the blade swings ahead of its normal position. This oscillation of the blades about the Vertical pin is especially dangerous when the craft is setting down on the deck of a floating Vessel rolling and pitching in rough seas.

Rotary Wing aircraft Operating under the aforedescribed conditions should, in order to avoid danger to its rotor blades, have some means to prevent the rotor blades from oscillatingf about their Vertical pivots when the rotor is being started or stopped. This means should, however, become inactive when the blades have reached the rotative speed where the centrifugal force is great enough to -maintain the blades in their correct radial position. It is, therefore, the principal object of this invention to provide such a device. i

Another object of this invention is vto provide means that will prevent any motion of the blades about their Vertical pivots during the period inwhich the rotor is turning too slowly to allow the'centrifugal force to maintain the blades in their correct radial position, said device being also provided with means.. to convert the looking mechanism into. a damperfor use parent in the following specification when read in conjunction with the drawings forming a part of this specification.

In Figure 1 of the drawings there is shown a rotor comprised of a hub, to which are hinged in a conventional manner the blades. The blades are hinged to the hub so that as they rotate with the hub, the blades are free to oscillate about their Vertical and horizontal hinges in response to forces acting on the blades. The blade links 8 are further provided with pitch bearings so that the blades may be adjusted about their pitching axis.

Figure 2 is a detailed view of my invention shown in cross-section. The arrangement of the parts in this view are such that the device is acting to prevent motion of the blade about. its Vertical pivot.

Figure 3 is a similar view except that the parts are shown in position wherein the device acts-as a blade clamper.

Referring more particularly to the drawings in which like numerals indicate like parts the preferred embodiment of the invention is shown as comprised of a housing ll of general tubular shape, the walls of which are provided with several oil passages. The housing ll is machined to receive a sleeve or cylinder 12 adapted to move longitudinally therein. The sleeve |2 forms a cylinder in which is carried a piston 13, the piston i3 is fixed to a piston rod [5 and provided with a suitable packing ring M. A cylinder head IG is formed as an integral part of the outer end of the sleeve |2 and is provided with central opening through which the piston rod |5 slides. The inner end of the sleeve 12 is closed by a member il threaded into the sleeve l2, said member |`l being provided with a central opening through which the inner end of the piston rod |5 passes. The member l 1 is also provided with an enlarged portion |8 which abuts against the shoulder |9 formed by counterboring the inner end of the housing ll when the sleeve is in its outer most position, as shown in Figure 3. The cylinder head 18 of sleeve |2 is provided with an enlarged portion 20 which acts to limit the inward movement of the sleeve |2 When it abuts the shoulder 2| formed by counter-boring the outer end of the housing II as shown in Figura 2. The sleeve 12 is urged inwardly by action of the spring 22 abutting against the cylinder head IG and held in place by a retaining member 23 threaded on the outer end of the housing ll.

The housing is provided with an oil inlet passage 25 said passage leading to several ports 26. 21 and 28 opening into the inside of the housing An oil outlet passage 29 is provided on the opposite side of the housing said passage being provided with ports 30, 3| and 32. The housing is also provided with two high pressure relief passages 33 and 34 containing high pressure relief valves 35 and 36. A damping conduit 31 is provided in the housing said conduit having at each end thereof inetering openings 38 and 39.

The sleeve |2 is provided with two inlet` ports., 40 and 4| spaced longitudinally so as to be in registry With the ports 21 and 28;when*the darnper.l is in looking position, as shown in'Figure 27. The sleeve |2 is provided with two high pressure relief ports 42 and 43 spaced so as to be in registry with the relief passages 33 and 34 when the damper,` is in damping position, as shown in Figura 3. The. sleeve |2 is also provided-with damping ports 44 and 45 which are located so as to begopposite of the metering openings 38 and whenthe damper is in damping position as shown in Figure 3; The member |1 has an annular recess 45 machined thereon to provide an oil passage connecting the port 26 with the port 3G.

The inner end of the housing is provided with a fork 41 for attachment to the bracketll formed on the pitch housing of the rotor blade link 8. The other end of the damper is connected to the bracket 49 formed on the inner portion of the blade by means of a pinextending through the eye formed on the outer end of the piston rod |5.

The inner end of the housing i is drilled to receive a stop pin 5| whichis movedzfrom "in and "out" positions by a centrifugally operated mein, ber 52 and by a spring 53'suitably carried on top of the housing The outer endof the housing is similarly drilled to receive a stop pin 54 which is also moved from "in" to "out" positions by a centrifugally operated member 55v and by a spring 56 carried on top of the housing Fluid under pressure is supplied to the inlet passage 25 from any suitable pressure source in any suitable manner such as shown in Patents 2,183,1'19 and 2264,943 to Agnew E. Larsen or Patent 2247,1)34 to H. F; Pitcairn.

Operation In operation the combination dampingv and looking device 41s installed as shown in Figure l, the outer end of the unit being connected to the blade spar and the inner end being connected to the blade link.

Oil is supplied by a suitable pump, to the inlet passage 25and returned to the pump by` a suitable conduit, not shown, connected to the outlet passage 29.

When `the rotor-is not rotating or Operating; at a low R.. P. M., the spring 22 forces the sleeve |2 to take the position shown in Figure 2. The sleeve |2 is locked in this position by the pin 5| which is urged downwardly by the spring' 53'. The spring 56 acts: to withdraw the stop pin'5' to allow; the sleeve |2 ,to locate itself in an inward position.-

Witlithe sleeve |2 in the position as shown in- Figure 2 oil entering the passage' 25 will b'e al-` lowed to fiow through the ports 49 and 4| and enter theV cylinder, moving the piston intoa centrally balanced position whereupon the oil will exhaust' out through the ports 3| and 3.2` into the passage 23 returning to the pump, not shown. Should the blade tend to 1ag about. its Vertical pivot itwill move the piston outwardly causing a partial1closureof `the exhaust port 32'. This will' cause the oil pressure to build up on that side of the piston returning the piston to its central position. Motion of the blade in an opposite direction Will be resisted in a similar manner as any partial closure of the port 3| will cause an unbalanceof the oil pressure acting on the piston to return it to its'central or balanced position.

When the rotor speed has been increased sufliciently to prevent excessive oscillation of the blades about their Vertical pins the centrifugal iorcezacting on the element 52 will be high enough toovercome the force of the spring 53, at which timthe-element will move the stop pin 5| upw'ardly allowing the centrifugal force acting on sleeve |2 tomove. it outwardly to the position shown in Figure 3 in which position it will be loc'kediby-thecentrifugal force acting on the elementicausing the lock pin 54 to move downwardly to the position shown in F'igure 3. When the sleeve |2 is moved outwardly to the aforedescribed'position itwill' be noted that the oil from the pump is shut off from the cylinder. and by-passed around the sleeve |2 through the conduit 46 and out through the passage 29 and returned to the pump. The high pressure oil trapped at either side of the piston |3 is allowed to circulate from one side of the pistonto the other throughmetering ports 38' and 39 located at thel ends of the passage 31.` This circulation of oil through the metering ports 38 and,39 allows the blade to oscillate slowly around its Vertical Pivot, said oscillation being damp'ed. Anyy excessive high,pressuregeneratedjby the motion of,

thepiston in the cylinder is relievedby pressure relief valves .35 and 3.6.

From theforegoing description it will be readily understood that this ,invention provides ameans to lock thebladesin a radial position When the rotor is turning, too slowly to generate enough centrifugal force on the blades to hold them in their correct radia! .poitions Ifthis is not donei the blades swing from an extreme advanced position to an extremeiagging position, -causing violent action of. the bladeslabout the pitclrbear- 1ng-,. asthe .Weight of the blades in either o fthese extreme positionsactslto move the 1:i tch'bea ringV housing about its axis. InV using a damper in combination with a, blade looking means, an lappreciable-A weight savingvis gained, overv the use of twoseparate devices o rdinarilyl required'to ac-A com-plish ;the ;functions of this invention.

Itiisto behndrstood-that while the foregoing isl a description ofjthe preferred'` embodiment'of' my inventionv as ShOWn in; the accompanying. draw-inggcertain changes. and modifications can.

be madwithout departingfrom the spiritvand scope o f this; mvention;

l. In combination, an articulated. sustaining rotor.a rotor blade damping and lockingdevice comprised'of a housing, the inner end ofsaid housing. having connecting means for attachmenttothe rotor.v hub a-fluid contain'ingcylinder carriedv by the'housing for longitudinal movementztherein, apiston slidably mountedin said cylinder, a shaft'extending through said cylinder and fixedto the piston'for reciprooation therewith, the outer end of said-shaft being provided with fastening. meansfor attachment to a rotor blade, a spring interposed between the outer end of. the-cylinder and a, cap secured to the outer end of the housing, said'spring acting to force the cylinder. inwardly against a stop formed in the housing, said housing being provided with an inlet oil'passage.V leading-to ports provided in the cylinder at opposite ends thereof, in registry therewith when the cylinder is in its inward position, said cylinder being provided with outlet ports spaced at each side of the piston when it is centrally located in the cylinder, said housing being provided with an outlet duct in registry with the outlet ports provided in the cylinder when the cylinder is in its inward position, said housing also being provided with a transfer duct opening into ports in registry therewith when the cylinder is in its outward position, provided near the ends of said cylinder, said device also being provided with centrifugally and spring actuated means to lock the cylinder in its inward position when the centrifugal forces are low or nonexistent and in its outward position when the centrifugal forces acting on the device are high.

2. In combination, a rotor comprised of a hub, a blade attached to said hub to permit the blade to oscillate in the plane of rotation, hydraulic means to move said rotor blade into a radial position with reference to the Vertical axis of the rotor and hold it in such a position when the centrifugal forces acting on the blade are not high enough to maintain such a radial position, said hydraulic means comprising a piston connected with said blade, a cylinder containing the piston, said cylinder being secured to the rotor hub, said cylinder being supplied at each end thereof with fluid under pressure, said cylinder having outlet ports centrally spaced therein in such relationship that if the piston is not centrally located it will act to cover one or the other of the outlet ports so that the fluid pressure acting on the piston will be unbalanced, said unbalance of pressure acting to move the piston to a central position where the fiuid outlets Will be opened to balance the pressure on each side of the piston and maintain it in said central position.

3. In combination, an aircraft sustaining rotor comprising a hub, a blade hinged to the hub to permit relative oscillation, hydraulic damper means comprising a cylinder and normally centralized piston having a rod, said cylinder and rod being connected between the hub and blade,

passages to deliver pressure fluid to opposite ends of the cylinder, two discharge ports in said cylinder both uncovered only when the piston is centralized and alternatively covered when the piston is displaced in either direction from its central position, a by-pass connecting opposite ends of the cylinder and having fiuid fiow restricting means therein, and a second by-pass communicating with said passages to directly waste pressure fluid, valve means normally biased to open said delivery passages and said discharge ports and close said first and second by-passes, said valve means being positioned and mounted to move by centrifugal force against said bias to open said by-passes and close said delivery passages and discharge ports.

4. The device of claim 3 in which biased lock means is provided to hold the valve in biased position and means responsive to centrifugal force effective at rotor speeds above the order of 30 percent of maximum to release said lock means whereby the valve may move .by eentrifugal force.

5. The device of claim 4 in which second lock means is provided to hold the valve in by-pass opening position, means biasing the second lock to open position and centrifugal force responsive means to close said second lock when the rotor speed exceeds the order of 30 percent of maximum.

JOSEPI-I RZECZYCKI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 11343262 Steiner Sept. 20, 1927 1,948,457 Larsen Feb. 20, 1934 1,951,483 Knapp et al. Mar. 20, 1934 2,048,326 Dyer et al July 21, 1936 2,102,027 Prewitt Dec. 14, 1937 2,318,259 Sikorsky May 4, 1943 2,465,681 Gluhareff Mar. 29, 1949 2,512,46l Jenny June 20, 1950 

